Spark arrester and silencer



March 30, 1937. R a BOURNE ET AL 2,075,264

SPARK ARRESTER AND SILENCER Filed April 3, 1935 2 Sheets-Sheet l 43 f Fl. A?

INVENTOR fol AM) .5. Boll/ME 41m BY Hum H. Mvx/M ATTORNEYS March 30, 1937. RB. BOURNE ET AL SPARK ARRESTER AND SILENCER Filed April 3, 1935 2 Sheets-Sheet 2 INVEN OR Rom/v0 1130mm: mm E/MM ffi Mum ATTORNEYS Patented Mar. 30, 1937 UNITED STATES SPARK ARRESTER AND SILENCEB Roland B. Bourne and Hiram H. Maxim, Hartford,

Conn., assignors to The Maxim Silencer Company, Hartford, Conn., a corporation of Connecticut Application April 3, 1935, Serial No. 14,522

11 Claims.

The exhaust gases from internal combustion engines, especially of the Diesel type, frequently contain live sparks, particles of carbon and the like. In many Diesel engine installations, it is 5 imperative to remove these solid particles from the exhaust gas and, at the same times, to effectively silence the accompanying exhaust noise.

The present invention accomplishes these results in a unique manner without recourse to the use of water as a quenching agent. The solid particles are eifectively separated out by centrifugal force and by gravity. Sound waves comprising the exhaust noise are attenuated by acoustic friction and by the acoustic reaction of side 15 branches suitably disposed and proportioned. A

unique feature disclosed in thepresent specification is the use of a mechanical separating means which also functions as an acoustic side branch whereby sound waves of predictable frequencies 20 are highly attenuated.

The invention will be better understood by referring to the drawings, in which Fig. 1 shows a sectional view of a preferred embodiment of the invention;

Fig. 2 shows a schematic device illustrating the acoustic principles involved in the separating chambers;

Fig. 3 shows a diagrammatic view of another embodiment of the invention; and

Figs. 4, 5 and 6 show other practical embodimerits of the invention.

Referring to Fig. 1, this embodiment comprises the cylindrical casing l0 having the top end closure II and the bottom end closure l2, in 35 which are formed respectively the outlet opening l3 and the eccentrically disposed inlet opening l4.

Studs l5 are shown for flange connecticns. The

most direct path through casing [0 from the inlet opening I 4 to the outlet opening i3 constitutes the main sound conducting channel, and

similarly in the other embodiments of the invention later described the main sound conducting channel is the most direct path between the corresponding inlet and outlet openings. A centrally disposed sound channel l6, formed by a tubular member ll, extends from a centrally disposed opening l8 in an intermediate partition l9 to the outlet opening I3. A transverse partition 20, located intermediate the partition l9 and the end closure H, and extending from the casing 10 to'the tubular conduit I1, divides the space extcrior to said conduit ll into the two compartments 2|, 22, which communicate with the sound channel l6 through openings 23, 24, in said conduit ll. It will be seen that that portion of the device between the headers II and I9 constitutes an acoustic channel having two acoustic side branches acoustically coupled thereto at inter- W vals along its length.

The lower chamber 25, into which the exhaust gases enter through the inlet opening ll, houses the dirt separating means which comprises a generally cone-shaped hopper 26 ailixed to the lower end of a short cylindrical member 21, and peripheral gas deflecting or spinner blades 26 extending from the inside of the member 21 to the outside of a coaxially disposed cylindrical member 29 which depends from the intermediate partition l9 and forms a relatively large channel 30 in series with the interior of the member 21 and the centrally disposed sound channel H5. The conical member 26 is so proportioned that the narrow bottom end thereof, which terminates in a short pipe 3|, extends through a suitable open ing in the bottom header i2 to one side of the inlet connection I4 so that the accumulated dirt in the bottom of the conical member 26 may be easily removed from time to time by unscrewing the cap 32. The spinner blades 28 and the passage 33 leading thereto are made accessible for occasional cleaning through the hand hole 34 placed in the casing I0. Cleaning of these passages may be necessary in some installations if excessive lubricating oil comes over in the exhaust. The exhaust gases enter the device through the bottom inlet l4 and are allowed to expand into the bottom chamber 25 exterior of the cone 26. They pass thence upward, through the tortuous passages formed by a simple baffle system 35, 36, thence through the annular passage 33, are deflected downward by the partition I9 and pass into the helical passages formed by the spinner blades 28 extending between the members 21 and 29 respectively. The exhaust gases, bearing the entrained sparks and other solid matter, are given a vigorous whirling motion in a downward direction whereby the solid matter is thrown against the inside surface of the conical member 26 and gradually drifts down to the bottom thereof in a generally spiral path. There is little tendency for the matter once separated to be again entrained, since the velocity of the exhaust gases within the conical member 26 and in the relatively large channel 30 is very low. Upon leaving the bottom end of the helical passes the exhaust gas bends upwardly into said large centrally disposed channel 30, since there is no egress for it in the member 26, and thence passes out, generally into a tail pipe through the outlet connection l3 by way of the channel I6, clean and silent. The separating conical hopper 26, being directly exposed to the full blast of incoming exhaust gases, must be made in such a manner that it will not rattle or ring and will not transmit sound directly through its walls. The member 26 is made up of a plurality of laminations of relatively thin sheet steel, as shown in Fig. 1, which construction renders the cone 26 acoustically dead and effectively prevents the transmission of sound from the bottom inlet chamber to the interior of the cone. It completely eliminates shell noise. Likewise, but 5 generally to a less degree, all other parts of the device are laminated to prevent ringing and transmission of sound to the outside of the casing ID. The baffles 35, 3B, are heavily laminated.

The acoustic behavior of the separating chamher comprising the cylinder 21 and the cone 26 is best understood by a consideration of the schematic device shown in Fig. 2. It comprises the generally cylindrical casing having perforate end closures at either end thereof. From a central opening in one end closure extends the centrally disposed conduit 41 of cross sectional area S1. The coaxially disposed cylinder 42 overlaps the conduit M to form a short annular channel 43, which, in the embodiment of Fig. l, is used 20 to impart a whirling motion to exhaust gases passing therethrough by means of helical baille members indicated at 44. These are like the blades 28 of Fig. 1 and need not be described in detail. The interiorly directed end of the cylinder 42 is aflixed to a cone 45 which extends to a point in adjacency to the inlet opening 46. It will thus be seen that there is acoustically coupled to the inside end of the conduit 4|, an acoustic side branch, partly in the form of a cylinder of cross sectional area S2 and partly in the form of a closed cone the base of which has the same area. The side branch does not begin at the actual end of the conduit 41 but at a distance H therefrom, a as shown by the dotted line 41. The remaining cylindrical section has an acoustic length L and is in series with the cone of acoustic length Le. The value of H, for many commercial embodiments of the invention is approximately .3R, R being the radius of the cylinder 42. This distance may also be expressed in terms of the end correction for the conduit 4 l. The acoustic side branch as described is of the linear type, wherein change of phase as a function of distance may take place, 45 and is therefore an appreciable portion of a wave length in length for the sound frequencies involved in its acoustic functioning. The main acoustic channel to which the side branch is acoustically coupled comprises the inlet opening 46, the annular passage 48 between the outside of the cone and cylinder and the inside of the casing 40, the annular passage 43 and the outlet conduit of cross sectional area S1. At the junction point between the sidebranch and the main channel, the latter is reflexed or folded back upon itself and thus affords a means for obtaining very close acoustic coupling between the channel and its associate side branch.

The acoustic impedance looking into the side branch so formed may be expressed by the following equation:

In the above equation the symbols have the following significances, which hold true al o 10; the

further equations below with the changes and additions there noted:

ZS=acoustic impedance looking into the side branch f=frequency of sound wave C=velocity of sound in the medium =density of the medium.

This equation may be used to determine the resonance frequencies for the side branch and to ascertain the frequency vs. attenuation characteristics thereof. Generally, in commercial practice, the distance L of Fig. 2 is made substantially zero. Under these conditions, Equation (1) reduces to Equation (2) is the expression for the impedance looking into the open end of a complete closed cone continued to the apex. The natural frequencies of resonance of such may be determined from wL 2T: 1, 2, 3, 4, etc. (3)

The sound frequencies so determined will be most highly attenuated by the conical sidebranch. For a more complete description of sound attenuating devices making use of conical sidebranches, reference is made to the United States patent to R. B. Bourne, 2,017,744, granted October 15, 1935. It will be seen that the conical hopper 26, Fig. l, in addition to serving as a dirt separator, is in fact an acoustic sidebranch, of acoustic length Le, functioning substantially as a true cone. The fact that the cone is not actually continued to a point apex is of slight importance, since the degree of deparature therefrom is relatively slight. Acoustic theory shows and experiment proves that the conical resonator maybe filled with solid matter for a distance equal to 25% of its length without changing its fundamental response frequency more than 5%. The reason for this is that as soon as the apex of the cone is filled, the sidebranch becomes a truncated cone, which responds to a lower frequency for a given length than does a complete cone continued to its apex. Thus, the act of filling up a cone from the apex does not seriously change its fundamental response frequency over a considerable range. In practice, the conical hopper is emptied at periodic intervals so that no great accumulation is permitted to take place. Likewise, the eccentricity of the cone is of minor importance acoustically. In practice, the sidebranches 2i and 22 are designed so that they attenuate bands of sound frequencies not highly attenuated by the conical sidebranch. This, of course, results in an over all attenuation-frequency characteristic covering a very wide band of frequencies in the low and intermediate frequency region. Sound waves of high frequency are attenuated by acoustic friction, either at or near the surfaces of passages, etc., or in the gas itself due to turbulence, pressure gradients, etc. Most of the high frequency attenuation takes place in the tortuous passages through the bailie system 35, 36.

In Fig. 3 we have shown in diagrammatic form a sectional view of another embodiment of the sound attenuating features.

invention, particularly designed for use in installations where an unusually large amount of dust or other solid matter is entrained in the gas or air discharge. The major difference between this form and that previously described is that two separating means are used in cascade and the separate sidebranches are dispensed with. This form of device comprises a casing provided with headers 5| and 52, the former of which has a discharge passage 53. The inlet passage 54 is in this case formed in one side of the main casing 50. A cone 55 is mounted within the lower part of the casing, merging at its top into a cylindrical section 56. Above this cone is an annular header 5'! having a downwardly depending flange 58 between which and the cylindrical section 56 are mounted helical spinner blades which are the same in general construction as those shown in Fig. 1 and which need not therefore be described in detail. Also mounted within the casing 5|! is a second cone 80. nested within the first and merging at its top into a cylindrical section 8|. A series of helical spinner blades 82 are secured between the inside of this cylindrical section and a cylindrical flange 63 projecting downwardly from the header 5|. The lower ends of both cones preferably project slightly beyond the bottom header 52, and are enclosed by one or more caps 64.

The path of the'gase's and the separation of the dust and dirt is shown by the arrows. Each conical separating chamber and its accompanying spinner system are essentially the same as that shown in Fig. 1. The acoustic lengths L1 and La of the two cones are chosen with regard to the sound frequencies to be attenuated. The bottom cone, of acoustic length Ll, although of annular cross section nevertheless functions as a true cone. This will be evident from the fact that, as can easily be shown, the cross sectional area varies with distance along its length in the same manner as does a true cone. Furthermore, the annular conical space may be considered to be the remainder when the volume of one cone is subtracted from the volume of another coaxially disposed cone, both cones having their apexes at a common point. The collected dirt in the bottoms of both cones may be removed simultaneously by removing the bottom end cap. This embodiment of the invention is preferably made with a bottom side inlet, as shown, in order to accommodate the longer cone more easily, although this teature is not absolutely essential. If desired, additional sound traps may be installed after the manner shown in Fig. 1. The embodiment shown in Fig. 3 offers somewhat higher attenuation for. sounds of high frequency than does that of Fig. 1, owing to the more tortuous path of the gases through the device, the additional spinner blades, etc. Hand holes 66 for cleaning and inspection purposes are provided.

Fig. 4 shows an embodiment of the invention having a simple construction and yet unique It comprises 9. cylindrical casing 18 having a top header 1| with an outlet connection 12 therein, and a bottom header with an inlet opening 18. Extending about half-way down from the header 1| is a centrally disposed conduit I4 which forms the channel 1! connecting with the outlet opening 12. This channel I5 terminates in an enlarged portion 18 formed by a short cylinder 11, the upper end of which is afllxed to an annular header 18 attached to the inner end of the conduit 14 as shown. Afllxed to the outer surface of the cylinder 11 are a plurality of spinner blades 19 in the annular channel 8| after the manner shown in Fig. 1. Said spinner system likewise forms a support for the cylinder 88 which in part identifies the helical passage 8| and in part the annular passage 82 between it and the casing 10. Said member 80 extends below the bottom of the spinner assembly a distance H as hereinbeiore described, and is afiixed to the upper end of the separating hopper 83 which extends downward through the bottom header 12' and is terminated in a removable end cap. The conical sidebranch 81, of acoustic length LC, attenuates sound irequencies in accordance with Equation (3). The space between the outside of the conduit I4 and the inside of the casing forms a closed annular sidebranch 85 of the linear type, of acoustic length L. This sidebranch begins at a distance H above the top of the spinner element and is closely coupled acoustically to both the annular channels 8| and 82 where they join. The acoustic coupling is seen to be similar in kind to that of the conical sidebranch 84. By making L=Lc, there will be afforded two overlapping recurring attenuation characteristics, whereby sound frequencies comprising a complete numerical series are highly attenuated. Since the two characteristics overlap, there will be no regions of zero attenuation. The sound frequencies suffering maximum attenuation may be determined from The dirt separating action and high frequency attenuating means is the same as described in connection with Fig. l. The hand hole 86 provides accessibility to the annular passage 82 and the spinner assembly 16.

Another embodiment of the invention functioning in a manner somewhat similar to that shown in Fig. 4, is shown in Fig. 5. The device is similar acoustically to thatoi Fig. 4, excepting for the transverse partition 80 which identifies the closed end of the annular linear sidebranch 9|. Said sidebranch 9| is acoustically coupled to the main channel 92, formed by the conduit 93. through an annular slot 93. A preferred arrangement is to make the acoustic length L of the annular sidebranch 9| equal to the acoustic length Le of the conical sidebranch Bl formed by the dirt separating hopper 95, in which case the attenuation peaks occur in accordance with Equation (4). The parts below the partition 90 are similar with the corresponding elements of the device of Fig. 1, and need not be described in detail. Since the sidebranch 8| is coupled to the channel 92 at a point in adjacency to the outlet opening 96, a tail pipe 91 is generally used. An inlet pipe 98 aflixed to the inlet opening in the bottom header is also shown. A drain 99 in the bottom of the sidebranch chamber provides for removal of accumulated condensate, etc. therefrom.

In some cases, the requirements of the installation of a Diesel engine demand that not only shall the final discharge be clean and free of sparks. etc., but also that an extraordinary degree of noise reduction be attained. The device shown schematically in Fig. 6 accomplishes these results. It comprises an acoustic wave filter functioning as disclosed in U. 8. Patent No.

1,910,672, and shown as section B in the drawings, together with a combination spark separator and acoustic sidebranch in accordance with the principles of the present invention, represented by section A in the drawings. The cylindrical casing I00, having an inlet opening MI and an outlet opening it)! is divided into two compartments or sections by the transverse partition N33. The acoustic wave filter B comprises the longitudinally disposed main acoustic channel I 04 having acoustically coupled thereto through the slots the two doublet acoustic sidebranches l06. This filter oil'ers very high attenu- 15 ation to a number of wide bands of frequencies separated by narrow pass bands. Excepting for the first pass band, which begins at zero frequency and continues to the first attenuation band, the centers of the pass bands normal to this filter occur at :g=-;I g: -1 etc. (5)

It will be seen that the passed frequencies are in simple integral relation or as 1:2:324. The combination spark arrester and acoustic sidebranch section A is constructed as in Fig. 1, and need not be described in detail. By making the scans-- tic length of the conical sidebranch equal to %L, as shown, saidsidebranch oifersh-igh attenuation to those frequencies otherwise passed by the filter of section B, namely those determined by Equation (5) above.

Dry spark arrester silencers of the type disclosed herein have proven of great value in the field, and can be made to sell at low cost. Experience has shown that the size of particles separated out of the exhaust gases vary in size, down to the fineness of flour.

We claim:

1. In a device of the class described, a main sound and gas conducting channel, a combined dirt collecting and frequency selective acoustic sidebranch disposed in shunt to a portion of said main channel, and one orftmore frequency selective acoustic sidebranches disposed in shunt to the main channel in spaced relation to the first named sidebranch, said second mentioned acous- 5 tie sidebranches offering high attenuation to sound frequencies for which said first mentioned sidebranch offers substantially less attenuation.

2. A combined dirt separator and sound attenuating device comprising a casing divided into 55 a lower compartment and an upper compartment, means positioned in said lower compartment to separate entrained dirt and the like from gas passing therethrough and to highly attenuate predeterminable sound frequencies occurring therein, and means positioned in said upper compartment to highly attenuate sound waves of frequencies not highly attenuated in said lower compartment.

3. A combined silencer and dirt separator for the exhaust of internal combustion engines comprising a main sound and gas conducting channel therethrough and a plurality of cone-like dirt collecting chambers disposed at intervals 70 along the length of said channel, one of said dirt collecting chambers being nested within another of said chambers, means exterior of said silencer for simultaneously cleaning said chambers, and means for projecting entrained solid 75 matter into said collecting chambers.

4. A combined silencer and dirt separator in accordance with claim 3 wherein each of said dirt collecting chambers is proportioned to function as an acoustic sidebranch and is acoustically coupled to said gas and sound conducting channel, whereby predeterminable sound frequencies are highly attenuated.

5. A combined silencer and dirt separator comprising a casing, two vertically mounted conelike chambers of different length coaxially nested one within the other and having their projected apexes at a common point exterior or the casing, a plurality of downward directed annular helical passages positioned at the upper open ends of each of said chambers. and means for causing exhaust gas to pass downwardly through one of said sets of helical passages before it passesdownwardly through the other of said sets of helical passages, said closed chambers function ing as closed acoustic sidebranches whereby predeterminable sound frequencies present in the gas stream passing through the device are highly attenuated.

6. A combined dirt separator and silencer comprising a casing, having a main sound and gas conducting channel passing therethrough, said channel comprising an upwardly directed annular passage communicating with the inlet of said silencer, said passage being adjacent the inner wall of said casing, a downwardly directed helical passage nested within said annular passage and a centrally disposed upwardly directed passage communicating with the outlet of' said silencer, a combined cone-like dirt chamber and acoustic sidebranch, disposed directly below said helical passage and an annular closed acoustic sidebranch of uniform cross sectional area throughout its length disposed above said helical passage whereby two sets of predeterminable sound frequencies occurring in said main channel are highly attenuated.

7. A combined dirt separator and silencer in accordance with claim 6 wherein said annular linear acoustic sidebranch is acoustically coupled to the upper end of said helical passage.

8. A combined dirt separator and silencer in accordance with claim 6 where said annular linear acoustic sidebranch is acoustically coupled to said centrally disposed upwardly directed passageway.

9. A combined dirt separator and silencer comprising a generally cylindrical casing, a transverse partition having a passage for gas therein, dividing the easing into upper and lower compartments, an acoustic wave filter in the upper compartment having pass bands. and a combined dirt separator and acoustic sidebranch in the lower compartment capable of highly attenuating sound frequencies corresponding to the said pass bands of said acoustic wave filter.

10. The invention in accordance with claim 9 wherein said combined dirt separator and acoustic sidebranch comprises a cone-like hopper opening to the exterior of said casing.

11. A combined dirt separator and silencer comprising a casing having a main sound and gas conducting channel passing therethrough, said channel comprising an upwardly directed annular passage communicating with the inlet of said silencer, said passage being adjacent the inner wall of said casing, a downwardly directed helical passage nested within said annular passage and a centrally disposed upwardly directed passage communicating with the outlet of said silencer, a combined cone-like dirt chamber and acoustic sidebranch disposed directly below said helical passage and an annular closed linear acoustic sidebranch of uniform cross sectional area throughout its length disposed above said helical passage, the acoustic lengths of said cone-like chamber and of said annular linear sldebranch being equal whereby two sets of predeterminable sound frequencies occurring in the main channel will be attenuated with one of said sets intermediate the other set.

ROLANl) n. BOURNE. 

